Methods in recent years for designing bi-aspherical type progressive-power lens(es) are disclosed in Patent Documents 1through 5, wherein the method of design involves dividing an element having progressive refractive power into a convex-surface side (object side) and a concave-surface side (eye side).
Patent Documents 2through 5 in particular propose reducing astigmatism by combining a progressive-addition surface (a surface having progressive refractive power) and a regressive-addition surface (a surface having regressive refractive power).
Alternatively, the inventors of the present invention proposed bi-aspherical type progressive-power lens(es) as disclosed in Patent Document 6.
This lens involves a method for resolving the elements of a surface having progressive refractive power into curvature in the vertical direction and curvature in the horizontal direction, and combining the effects of the convex surface and the concave surface. The lens is configured so that the refractive surface elements of the prescription surface and the elements of the remaining object-side surface, which is different for each addition power, are disposed on the eye side.
The method for processing the refractive surface of a lens having progressive refractive power employs a method called the semi-finish lens method in order to reduce the overall processing cost and manufacture time. In this method, a halfway-processed lens blank (referred to hereinafter as a “semi-lens”) is prepared. This blank is composed of a surface that has already been processed (molded) into the final shape on one side and an incompletely processed surface on the other side. A semi-lens having the optimal curve according to the design specifications is selected from a previously prepared group of semi-lenses based on the ordered prescription, and the incompletely processed surface is processed. Selecting the shape and the concavity or convexity of the incompletely processed surface is decided by the manufacturer at the design stage.
Since a lens having progressive refractive power is provided with an addition power according to the prescription, semi-lenses are prepared with curves designed in accordance with the established range of addition powers relative to a basic design curve (a base curve). With an established addition power range of 0.5 to 3.50 diopters, for example, semi-lenses with thirteen different types of design curves are prepared if classified into groups in increments of 0.25 diopter. (In the specification of the present invention, designs for lenses having progressive refractive power are regarded as a single overall technical concept, as above, and lenses with prescriptions ranging from far-sighted presbyopia to near-sighted presbyopia (including lenses wherein the diopter range for distance vision extends from positive to negative as well as 0.00 diopters) are referred to as “lenses having progressive refractive power.”)
[Patent Document 1] Domestic re-publication of PCT international publication W097/19383
[Patent Document 2] Japanese Laid-open Patent Publication No. 2000-249992
[Patent Document 3] Published Japanese translation of PCT international publication No. 2002-539499
[Patent Document 4] Published Japanese translation of PCT international publication No. 2003-500685
[Patent Document 5] Published Japanese translation of PCT international publication No. 2004-524582
[Patent Document 6] Japanese Laid-open Patent Publication No. 2000-344813